Seeing

he tiptoed lest guard ……her.这里用hears ,may have hear ,will hear ,should hear 哪一个？别问为啥he和her，这是一道题，我也不知道为啥

meeting is better here.

Seeing

两个看来都用原型。有没有老师帮忙看看

fucking

look forward to 接动名词，所以选 seeing。

I look forward to ……u at the convocation.这里用seeing, meeting, joining都可以。还有很多词

The actual problem in this case is, that "to" is a preposition here and NOT part of the infinitive! Therefore the Gerund is required.

He tiptoed(,) lest THE guard should hear her.